Did you enable it to run at startup? That's probably the most likely cause, as I can't think of anything else that would cause this.
I don't have iTunes installed on my laptop, but there is a way to stop it running at startup if it is enabled. A.
1. In start menu search, type in "msconfig", and press 'Ctrl' + 'Shift' + 'Enter'.
2. In the startup tab, uncheck 'iTunes' or similar if it is there.
3. Press OK.
4. If prompted, reboot.
If that is not the case, I will alert other experienced members here